In the course of our investigation on bioactive compounds from marine microorganisms, actinomycetes strains AAR 1-1 and AAR 14 associated with a bluish purple and a purplish white marine sponges, respectively, from Adang-ravee Island showed interesting antimicrobial activity. Based on morphological, cultural, physiological, and biochemical characteristic studies, the strains AAR 1-1 and AAR 14 were identified as the genus Streptomyces. The bioassary-directed fractionation, using antimicrobial activity against Staphylococcus aureus ATCC 25923, of the ethyl acetate extract from the fermentation broth of the strain AAR 1-1 led to the isolation of a known compound, actinomycin D. Directed by antimicrobial activity against Candida albicans ATCC 10231, fractionation of the methonol extract from the fermentation broth of the strain AAR 14 yielded two known diketopiperazines, cyclo-(L-prolyl-D-leucyl) and cyclo-(L-prolyl-D-valyl), one acetamide derivative, N-[2'-(4''-hydroxyphenyl)ethyl] acetamide, and a mixture of three new members of antimycins containing two major components, antimycins B[subscript 1] and B[subscript 2], together with a minor component, antimycin B[subscript 3]. The structure elucidation of these compounds was achieved by analyses of UV, IR, MS, [superscript 1]H, and [superscript 3]C NMR spectral data as well as comparison with the literatures. The isolated actinomycin D showed antimicrobial activity against S. aureus ATCC 15923 and Bacillus subtilis ATCC 6633, antimalarial activity against Plasmodium falciparum (K1 multi-drug resistant strain), cytotoxic activity against oral human epidermoid carcinoma cell lines and breast cancer cell lines, and antituberculous activity against Mycobacterium tuberculosis H37Ra. Two diketopiperazines showed fungistatic activity against C. albicans ATCC 10231.
